Belief

Contemporary analytic philosophers of mind generally use the term
“belief” to refer to the attitude we have, roughly,
whenever we take something to be the case or regard it as true. To
believe something, in this sense, needn't involve actively reflecting
on it: Of the vast number of things ordinary adults believe, only a
few can be at the fore of the mind at any single time. Nor does the
term “belief”, in standard philosophical usage, imply any
uncertainty or any extended reflection about the matter in question
(as it sometimes does in ordinary English usage). Many of the things
we believe, in the relevant sense, are quite mundane: that we have
heads, that it's the 21st century, that a coffee mug is on the desk.
Forming beliefs is thus one of the most basic and important features
of the mind, and the concept of belief plays a crucial role in both
philosophy of mind and epistemology. The “mind-body
problem”, for example, so central to philosophy of mind, is in
part the question of whether and how a purely physical organism can
have beliefs. Much of epistemology revolves around questions about
when and how our beliefs are justified or qualify as knowledge.

Most contemporary philosophers characterize belief as a
“propositional attitude”. Propositions
are generally taken to be whatever it is that sentences express
(see the entry on
propositions). For example,
if two sentences mean the same thing (e.g., “snow is white” in
English, “Schnee ist weiss” in German), they express the same
proposition, and if two sentences differ in meaning, they express
different propositions. (Here we are setting aside some
complications about that might arise in connection with indexicals;
see the entry on
indexicals.)
A propositional attitude, then, is the mental state of
having some attitude, stance, take, or opinion about a proposition or
about the potential state of affairs in which that proposition is
true—a mental state of the sort canonically expressible in the
form “SA that P”, where S picks
out the individual possessing the mental state, A picks out
the attitude, and P is a sentence expressing a
proposition. For example: Ahmed [the subject] hopes [the attitude]
that Alpha Centauri hosts intelligent life [the proposition], or
Yifeng [the subject] doubts [the attitude] that New York City will
exist in four hundred years. What one person doubts or hopes, another
might fear, or believe, or desire, or intend—different
attitudes, all toward the same proposition. Contemporary discussions
of belief are often embedded in more general discussions of the
propositional attitudes; and treatments of the propositional attitudes
often take belief as the first and foremost example.

It is common to think of believing as involving
entities—beliefs—that are in some sense contained in the
mind. When someone learns a particular fact, for example, when Kai
reads that astronomers no longer classify Pluto as a planet, he
acquires a new belief (in this case, the belief that astronomers
no longer classify Pluto as a planet). The fact in question—or
more accurately, a representation, symbol, or marker of that
fact—may be stored in memory and accessed or recalled when
necessary. In one way of speaking, the belief just is the fact or
proposition represented, or the particular stored token of that fact
or proposition; in another way of speaking, the more standard in
philosophical discussion, the belief is the state of having such a
fact or representation stored. (Despite the ease with which we slide
between these different ways of speaking, they are importantly
distinct: Contrast the state of having hot water in one's water
heater—the state of being “hot-water ready”, say—with the
stuff actually contained in the heater, that particular mass of water,
or water in general.)

It is also common to suppose that beliefs play a causal role in the
production of behavior. Continuing the example, we might imagine that
after learning about the demotion of Pluto, Kai naturally
turns his attention elsewhere, not consciously considering the
matter for several days, until when reading an old science textbook
he encounters the sentence “our solar system contains nine
planets”. Involuntarily, his new knowledge about Pluto is called up
from memory. He finds himself doubting the truth of the textbook's
claim, and he says, “actually, astronomers no longer accept that”. It
seems plausible to say that Kai's belief about Pluto, or his
possession of that belief, caused, or figured in a causal explanation
of, his utterance.

Various elements of this intuitive characterization of belief have
been challenged by philosophers, but it is probably fair to say that
the majority of contemporary philosophers of mind accept the bulk of
this picture, which embodies the core ideas of the
representational approach to belief, according to which
central cases of belief involve someone's having in her head or mind a
representation with the same propositional content as the belief. (But
see §2.2, below, for some caveats, and see the entry on
mental representation.)
As discussed below, representationalists may diverge in their
accounts of the nature of representation, and they need not agree
about what further conditions, besides possessing such a
representation, are necessary if a being is to qualify as having a
belief. Among the more prominent advocates of a representational
approach to belief are Fodor (1975, 1981, 1987, 1990), Millikan (1984,
1993), Dretske (1988), Cummins (1996), and Burge (2010).

One strand of representationalism, endorsed by Fodor, takes mental
representations to be sentences in an internal language of
thought. To get a sense of what this view amounts to, it is
helpful to start with an analogy. Computers are sometimes
characterized as operating by manipulating sentences in “machine
language” in accordance with certain rules. Consider a simplified
description of what happens as one enters numbers into a
spreadsheet. Inputs from the keyboard cause the computer, depending on
the programs it is running and its internal state, to instantiate or
“token” a sentence (in machine language) with the content (translated
into English) of, for example, “numerical value 4 in cell A1”. In
accordance with certain rules, the machine then displays the shape “4”
in a certain location on the monitor, and perhaps, if it is
implementing the rule “the values of column B are to be twice the
values of column A”, it tokens the sentence “numerical value 8 in cell
B1” and displays the shape “8” in another location on the monitor. If
we someday construct a robot whose behavior resembles that of a human
being, we might imagine it to operate along broadly the lines
described above—that is, by manipulating machine-language sentences
in accordance with rules, in connection with various potential inputs
and outputs. Such a robot might somewhere store the machine-language
sentence whose English translation is “the chemical formula for water
is H2O”. We might suppose this robot is able to act as does
a human who possesses this belief because it is disposed to access
this sentence appropriately on relevant occasions: When asked “of what
chemical elements is water compounded?”, the robot accesses the water
sentence and manipulates it and other relevant sentences in such a way
that it produces a human-like response.

According to the language of thought hypothesis (see the entry on the
language of thought hypothesis),
our cognition proceeds rather like such a robot's. The formulae we
manipulate are not in “machine language”, of course, but rather in a
species-wide “language of thought”. A sentence in the language of
thought with some particular propositional content P is a
“representation” of P. On this view, a subject believes that
P just in case she has a representation of P that
plays the right kind of role—a “belief-like” role—in her
cognition. That is, the representation must not merely be instantiated
somewhere in the mind or brain, but it must be deployed, or apt to be
deployed, in ways we regard as characteristic of belief. For example,
it must be apt to be called up for use in theoretical inferences
toward which it is relevant. It must be ready for appropriate
deployment in deliberation about means to desired ends. It is
sometimes said, in such a case, that the subject has the proposition
P, or a representation of that proposition, tokened in her
“belief box” (though of course it is not assumed that there is any
literal box-like structure in the head).

Dretske's view centers on the idea of representational systems as
systems with the function of tracking features of the world (for a
similar view, see Millikan 1984, 1993). Organisms, especially mobile
ones, generally need to keep track of features of their environment to
be evolutionarily successful. Consequently, they generally possess
internal systems whose function it is to covary in certain ways with
the environment. For example, certain marine bacteria contain internal
magnets that align with the Earth's magnetic field. In the northern
hemisphere, these bacteria, guided by the magnets, propel themselves
toward magnetic north. Since in the northern hemisphere magnetic north
tends downward, they are thus carried toward deeper water and
sediment, and away from toxic, oxygen-rich surface water. We might
thus say that the magnetic system of these bacteria is a
representational system that functions to indicate the direction of
benign or oxygen-poor environments. In general, on Dretske's view, an
organism can be said to represent P just in case that
organism contains a subsystem whose function it is to enter state
A only if P holds, and that subsystem is in state
A.

To have beliefs, Dretske suggests, is to have an integrated manifold
of such representational systems, acquired in part through associative
learning, poised to guide behavior. Given the lack of such a
complex, and the lack of associative learning, magnetosome bacteria
cannot, on Dretske's view, rightly be regarded as literally possessing
full-fledged beliefs. But exactly how rich an organism's
representational structure must be for it to have beliefs, and in what
ways, Dretske does not address, regarding it as a terminological
boundary dispute, rather than a matter of deep ontological
significance. (For more on belief in non-human animals see §4
below.)

Recent representational approaches sometimes especially emphasize
the normative dimension of belief. That is, they emphasize the idea
that it is central to a mental state's being a belief as
opposed to some other mental state (e.g., a supposition, an imagining,
a desire) that it is necessarily defective in a certain way if it is
false. Shah and Velleman (2005) argue that conceiving of an attitude
as a belief that P entails conceiving of it as governed by a
norm of truth, that is, as an attitude that is correct if and
only if P is true. Similarly, Burge (2010) argues that the
"primary constitutive function" of believing is the production of
veridical propositional representations. (See also the literature on
"direction of fit": Anscombe 1957/1963; Searle 1983; and on norms of
belief generally: Chan, ed. 2013.)

If one accepts a representational view of belief, it's plausible to
suppose that the relevant representations are structured in
some way—that the belief that P & Q, for
instance, shares something structurally in common with the belief that
P. To say this is not merely to say that the belief that
P & Q has the following property: It cannot be
true unless the belief that P is true. Consider the following
possible development of Dretske's representational approach: An
organism has developed a system that functions to detect whether
P is or is not the case. It's supposed to enter state alpha
when P is true; its being in alpha has the function of
indicating P. Also, the organism has developed a separate
system for detecting whether P & Q is the
case. It's supposed to enter state beta when P &
Q is true; its being in beta has the function of indicating
P & Q. But alpha and beta have nothing important
in common other than what, in the outside world, they are supposed to
represent; they have no structural similarity; one is not compounded
in part from the other. Conceivably, all our beliefs could be set up
in this way, having as little in common as alpha and beta—one
internally unstructured representational state after another. To say
that mental representations are structured is in part to deny that our
minds work like that.

Among the reasons to suppose that our representations are structured,
Fodor argues, are the productivity and systematicity
of thought (Fodor 1987; Fodor and Pylyshyn 1988; Aizawa 2003). Thought
and belief are “productive” in the sense that we can
potentially think or believe an indefinitely large number of things:
that elephants despise bowling, that 245 + 382 = 627, that river
bottoms are usually not composed of blue beads. If representations are
unstructured, each of these different potential beliefs must, once
believed, be an entirely new state, not constructed from
representational elements previously available. Similarly, thought and
belief are “systematic” in the sense that an organism who
thinks or believes that Mengzi repudiated Gaozi will normally also
have the capacity (if not necessarily the inclination) to think or
believe that Gaozi repudiated Mengzi; an organism who thinks or
believes that dogs are insipid and cats are resplendent will normally
also have the capacity to think or believe that dogs are resplendent
and cats are insipid. If representations are structured, if they have
elements that can be shuffled and recombined, the productivity and
systematicity of thought and belief seem naturally to
follow. Conversely, someone who holds that representations are
unstructured has, at least, some explaining to do to account for these
features of thought. (So also, apparently, does someone who denies
that belief is underwritten or implemented by a representational
system of any sort.)

Supposing representations are structured, then, what kind of
structure do they have? Fodor notes that productivity and
systematicity are features not just of thought but also of language,
and concludes that representational structure must be linguistic. He
endorses the idea of an innate, species-wide language of thought (as
discussed briefly in §1.1 above); others tie the structure more
closely to the thinker's own natural (learned) language (Harman 1973;
Field 1978; Carruthers 1996). However, still others assert that the
representational structure underwriting belief isn't language-like at
all.

A number of philosophers have argued that our cognitive
representations have, or can have, a map-like rather than a
linguistic structure (Lewis 1994; Braddon-Mitchell and Jackson 1996,
Camp 2007; Rescorla 2009; though see Blumson 2012 and Johnson
forthcoming for concerns about whether map-like and language-like
structures are importantly distinct). Map-like representational
systems are both productive and systematic: By recombination and
repetition of its elements, a map-like representational system can
represent indefinitely many potential states of affairs; and a
map-like system that has the capacity, for example, to represent the
river as north of the mountain will normally also have the capacity to
represent, by a re-arrangement of its parts, the mountain as north of
the river. Although maps may sometimes involve words or symbols,
nothing linguistic seems to be essential to the nature of map-like
representation: Some maps are purely pictorial or combine pictorial
elements with symbolic elements, like coloration to represent
altitude, that we don't ordinarily think of as linguistic.

The maps view makes nice sense of the fact that when a person changes
one belief, a multitude of other beliefs seem also to change
simultaneously and effortlessly: If you shift a mountain farther north
on a map, for example, you immediately and automatically change many
other aspects of the representational system (the distance between the
mountain and the north coast, the direction one must hike to go from
the mountain to the oasis, etc.). In contrast, if you change the
linguistic representation “the mountain peak is 15 km north of
the river” to “the mountain peak is 20 km north of the
river”, no other representation necessarily changes: It takes a
certain amount of inferential work to ramify the consequences
through the rest of the system. Since it doesn't seem like we're
constantly making such a plethora of inferences, the maps view might
have an advantage here. On the other hand, though, perhaps just
because the linguistic view requires inference for what appears to
happen automatically on the maps view, it can better account for
failures of rationality, in which not all the necessary changes are
made and the subject ends up with an inconsistent view. Indeed
generally speaking it's unclear how the map view can accommodate
inconsistent beliefs unless one allows a proliferation of maps, with
the complications that ensue (like redundancy and mechanisms for
relating the maps). Certain sorts of indeterminacy may also be more
difficult to accommodate in map-like than in language-like
structures. A linguistic representation like “there are some
lakes east of the mountain” can leave completely unspecified how
many lakes, of what shape, and where; a map does not, it seems, as
easily do this. One further point of apparent difference between the
two views will be discussed in §2.2 below. Generally speaking,
one might worry that the maps view overgenerates and
overspecifies beliefs, while the linguistic view
undergenerates and underspecifies them.

A third and very different way of thinking about representational
structure arises from the perspective of connectionism, a
position in cognitive science and computational theory. According to
connectionism, cognition proceeds by activation streaming through a
series of “nodes” connected by adjustable
“connection weights”—somewhat as neural networks in
the brain can have different levels of activation and different
strengths of connection between each other. It is sometimes suggested
(e.g., by van Gelder 1990; Smolensky 1995) that the structure of
connectionist networks is representational but non-linguistic; and
perhaps so also is our representational structure. However, it would
take us too far afield to enter this technical issue here. (For more
on this topic see the entry on
connectionism.)

While representationalists like Fodor, Drestke, and
Jackson contend that having the right internal, representational
structure is essential to having beliefs, another group of
philosophers treats the internal structure of the mind as of only
incidental relevance to the question of whether a being is properly
described as believing. One way to highlight the difference
between this view and representationalism is this: Imagine that we
discover an alien being, of unknown constitution and origin, whose
actual behavior and overall behavioral dispositions are perfectly
normal by human standards. “Rudolfo”, say, emerges from a
spacecraft and integrates seamlessly into U.S. society, becoming a tax
lawyer, football fan, and Democratic Party activist. Even if we know
next to nothing about what is going on inside his head, it may seem
natural to say that Rudolfo has beliefs much like ours—for example,
that the 1040 is normally due April 15, that a field goal is worth 3
points, and that labor unions tend to support Democratic
candidates. Perhaps we can coherently imagine that Rudolfo does not
manipulate sentences in a language of thought or possess internal
representational structures of the right sort. Perhaps it is
conceptually, even if not physically, possible that he has no complex,
internal, cognitive organ, no real brain. But even if it is granted
that a creature must have human-like representations in order to
behave thoroughly like a human being, one might still think that it is
the pattern of actual and potential behavior that is
fundamental in belief—that representations are essential to belief
only because, and to the extent to, they ground such a
pattern. Dispositionalists and interpretationists
are drawn to this way of thinking.

Traditional dispositional views of belief assert that for someone to
believe some proposition P is for that person to possess one
or more particular behavioral dispositions pertaining to
P. Often cited is the disposition to assent to utterances of
P in the right sorts of circumstances (if one understands the
language, wishes to reveal one's true opinion, is not physically
incapacitated, etc.). Other relevant dispositions might include the
disposition to exhibit surprise should the falsity of P make
itself evident, the disposition to assent to Q if one is
shown that P implies Q, and the disposition to
depend on P's truth in executing one's plans. Perhaps all
such dispositions can be brought under a single heading, which is,
most generally, being disposed to act as though P is the
case. Such actions are normally taken to be at least pretty good
prima facieevidence of belief in P; the
question is whether being disposed, over all, so to act is
tantamount to believing P, as the dispositionalist
thinks, or whether it is merely an outward sign of belief. Braithwaite
(1932–1933) and Marcus (1990) are prominent advocates of the
traditional dispositional approach to belief (though Braithwaite
emphasizes in his analysis another form of belief, rather like
“occurrent” belief as described in §2.1 below).

There are two standard objections to traditional dispositional
accounts of belief. The first, tracing back at least to Chisholm
(1957), assumes that the dispositionalist's aim is to reduce
or analyze facts about belief entirely into facts about
outward behavior, facts specifiable without reference to other
beliefs, desires, inner feelings, and so forth (see the entry on
philosophical
behaviorism).
Such a reduction or analysis appears impossible for the following
reason: People with the same belief may behave very differently,
depending on their other beliefs, desires, and so forth. For example,
a person who believes that it will rain will only be disposed to take
an umbrella if she also believes that the umbrella will ward off the
water and if she doesn't want to get wet. Change the surrounding
beliefs and desires and very different behavior may result. A
dispositionalist attempting to specify the particular behavioral
dispositions associated with, for example, the belief that it's
raining will then either get it wrong about the dispositions of some
people (such as those who like to get wet) or will be forced to
incorporate into her dispositional analysis conditional antecedents
invoking the very ideas she is trying to analyze or reduce
away—saying, for example, that the person who believes that
P will behave in such-and-such a way if she believes
X and desires Y—apparently dooming the
reductionist project. (It may be possible to avoid this objection by
invoking a “Ramsey”-like approach to the reduction
[see the section on
Functional States and Ramsey Sentences in the entry on
functionalism
and Lewis 1972], but this type of analysis was not widely discussed
until after traditional dispositional approaches to belief had gone
largely out of fashion.)

The second standard objection to traditional dispositional accounts
of belief is to note the loose connection between belief and behavior
in some cases—for example, in a recently paralyzed person, or in
someone who wants to keep a private opinion (e.g., a Muscovite who
believes, in 1937, that Stalin's purges are morally wrong), or in
matters of very little practical relevance (e.g., an American
homebody's belief that there is at least one church in Nice). Again,
the traditional dispositionist seems faced with a choice between
oversimplifying (and thus mischaracterizing some people's
dispositions) and loading the dispositions with potentially
problematic or unwieldy conditional antecedents (e.g., he'd get the
umbrella if his paralysis healed; he'd speak up if
the political climate changed). On the other hand, however, the demand
for an absolutely precise specification of the conditions
under which a disposition will be manifested, without exception, may
be excessive. As Cartwright (1983) has noted, even perfectly
respectable claims in the physical sciences often hold only
ceteris paribus or “all else being equal”.

In light of these concerns and others, most recent philosophers
sympathetic with the view described in the first paragraph of this
section have abandoned traditional dispositionalism. They divide into
roughly two classes, which we may call liberal
dispositionalists and interpretationists. Liberal
dispositionalists avoid the first objection by abandoning the
reductionist project associated with traditional
dispositionalism. They permit appeal to other mental states in
specifying the dispositions relevant to any particular
belief—including other beliefs and desires. They also broaden
the range of dispositions considered relevant to the possession of a
belief so as to include at least some dispositions to undergo private
mental episodes that do not manifest in outwardly observable
behavior—dispositions, for example, for the subject to feel (and
not just exhibit) surprise should she discover the falsity of
P, for her privately to draw conclusions from P, to
feel confidence in the truth of P, to utter P
silently to herself in inner speech, and so forth. This appears also
to mitigate the second objection to some extent: The Muscovite
possesses his belief about Stalin's purges at least as much in virtue
of the things he says silently to himself and the disapproval he
privately feels as in virtue of his disposition to express that
opinion were the political climate to change. Advocates of views of
this sort include Price (1969), Audi (1972), Baker (1995),
Schwitzgebel (2002, 2013), and arguably Ryle (1949) (though Baker
characterizes her view in terms of conditional statements rather than
dispositions).

However, a philosopher approaching belief with the specific goal of
defending physicalism or materialism—the view that
everything in the world, including the mind, is wholly physical or
material (see
physicalism)—might have reason to
be dissatisfied with liberal dispositionalism, for the very reason
that it abandons the reductionist project. Although liberal
dispositional accounts of belief are consistent with physicalism, they
do not substantially advance that thesis, since they relate
belief to other mental states that may or may not be seen as
physical. The defense of physicalism was one of the driving forces in
philosophy of mind in the period during which the most influential
approaches to belief in contemporary analytic philosophy of mind were
developed—the 1960s through the 1980s—and it was one of
the principal reasons philosophers were interested in accounts of
propositional attitudes such as belief. Consequently, the failure of
liberal dispositionalism to advance the physicalist thesis might
be seen as an important drawback.

Interpretationism shares with dispositionalism the emphasis on
patterns of action and reaction, rather than internal representational
structures, but retains the focus, abandoned by the liberal
dispositionalist, on observable behavior—behavior
interpretable by an outside observer. Since behavior is widely assumed
to be physical, interpretationism can thus more easily be seen as
advancing the physicalist project. The two most prominent
interpretationists have been Dennett (1978, 1987, 1991) and Davidson
(1984; see
Donald Davidson).

To gain a sense of Dennett's view, consider three different methods
we can use to predict the behavior of a human being. One method, which
involves taking what Dennett calls the “physical stance”, is to apply
our knowledge of physical law. We can predict that a diver will trace
a roughly parabolic trajectory to the water because we know how
objects of approximately that mass and size behave in fall near the
surface of the Earth. A second method, which involves taking the
“design stance”, is to attribute functions to the system or its parts
and to predict that the system will function properly. We can
predict that a jogger's pulse will increase as she heads up the hill
because of what we know about exercise and the proper function of the
circulatory system. A third method, which involves taking the
“intentional stance”, is to attribute beliefs and desires to the
person, and then to predict that he will behave rationally, given
those beliefs and desires. Much of our prediction of human behavior
appears to involve such attribution (though see Andrews 2012).
Certainly, treating people as mere physical bodies or as biological
machines will not, as a practical matter, get us very far in
predicting what is important to us.

On Dennett's view, a system with beliefs is a system whose behavior,
while complex and difficult to predict when viewed from the physical
or the design stance, falls into patterns that may be captured with
relative simplicity and substantial if not perfect accuracy by means
of the intentional stance. The system has the particular belief that
P if its behavior conforms to a pattern that may be
effectively captured by taking the intentional stance and attributing
the belief that P. For example, we can say that Heddy
believes that a hurricane may be coming because attributing her that
belief (along with other related beliefs and desires) helps reveal the
pattern, invisible from the physical and design stances, behind her
boarding up her windows, making certain phone calls, stocking up
provisions, etc. All there is to having beliefs, according to Dennett,
is embodying patterns of this sort. Dennett acknowledges that his view
has the unintuitive consequence that a sufficiently sophisticated
chess-playing machine would have beliefs if its behavior is very
complicated from the design stance (which would involve appeal to its
programmed strategies) but predictable with relative accuracy and
simplicity from the intentional stance (attributing the desire to
defend its queen, the belief that you won't sacrifice a rook for a
pawn, etc.).

Davidson also characterizes belief in terms of practices of belief
attribution. He invites us to imagine encountering a being with a
wholly unfamiliar language and then attempting the task of
constructing, from observation of the being's behavior in its
environment, an understanding of that language (e.g., 1984, p.
135–137). Success in this enterprise would necessarily involve
attributing beliefs and desires to the being in question, in light of
which its utterances make sense. An entity with beliefs is a being for
whom such a project is practicable in principle—a being that emits,
or is disposed to emit, a complex pattern of behavior that can
productively be interpreted as linguistic, rational, and expressive of
beliefs and desires.

Dennett and Davidson both endorse the “indeterminacy” of belief
attributions: In at least some cases, multiple incompatible
interpretive schemes may be equally good, and thus there may be no
fact of the matter which of those schemes is “really” the correct one,
and thus whether the subject “really” believes P, if belief
that P is attributed by one scheme but not by the other.

Many philosophers identify themselves as functionalists (see
functionalism)
about mental states in general or belief in particular.
Functionalism about mental states is the view that what makes
something a mental state of a particular type are its actual and
potential, or its typical, causal relations to sensory stimulations,
behavior, and other mental states (seminal sources include Armstrong
1968; Fodor 1968; Lewis 1972, 1980; Putnam 1975; Block
1978). Functionalists generally contrast their view with the view that
what makes something a mental state of a particular type are facts
about its internal structure. To understand this distinction, it may
be helpful to begin with some non-mental examples. Arguably, what
makes something a streptococcal bacterium, or a cube, is its shape or
internal structure; its causal history or proneness to produce
particular effects on particular occasions is only secondarily
relevant, if at all. In contrast, whether something is a hard drive or
not is not principally a matter of internal structure. A hard drive
could be made of plastic or steel, employ magnetic tape or
lasers. What matters are the causal relationships it's prone to enter
with a computer: Under certain promptings, it enters states such that,
under certain further promptings, it will generate outputs of a
certain sort. Internal structure is relevant only secondarily, insofar
as it grounds these causal capacities. Likewise, according to the
functionalist, what makes a state pain is not its particular
neural configuration. People and animals with very different neural
configurations could all equally be in pain (even, conceivably, a
Martian with an internal structure radically different from ours could
suffer pain). What matters is that the subject is in a state that
(roughly) is apt to be caused by tissue damage or tissue stress and
that, in turn, is apt to cause signs of distress, withdrawal, future
avoidance of the painful stimulus, and (in verbal subjects) thoughts
and utterances like “that hurts!”.

Philosophers frequently endorse functionalism about belief
without even briefly sketching out the various particular functional
relationships that are supposed to be involved, though Loar (1981) is a
notable exception to this tendency. However, among the causal
relationships contemporary analytic philosophers have often seen as
characteristic of belief are the following (these are sketched here
only roughly; they come in many versions differing in nuance):

(1) Reflection on propositions (e.g., [Q] and [if Q
then P]) from which P straightforwardly follows, if
one believes those propositions, typically causes the belief that
P.

(2) Directing perceptual attention to the perceptible properties of
things, events, or states of affairs, in conditions favorable to
accurate perception, typically causes the belief that those things,
events, or states of affairs have those properties (e.g., visually
attending to a red shirt in good viewing conditions will typically
cause the belief that the shirt is red).

(3) Believing that performing action A would lead to event
or state of affairs E, conjoined with a desire for E
and no overriding contrary desire, will typically cause an intention
to do A.

(4) Believing that P, in conditions favoring sincere
expression of that belief, will typically lead to an assertion of
P.

Loar emphasizes versions of (2) and (3) over (1) and (4), but one
sees conditions of this sort at least briefly alluded to by a number
of functionalist philosophers, including Dennett (1969, 1978),
Armstrong (1973), Stalnaker (1984), Fodor (1990), Pettit (1993), and
Shoemaker (2003). For the functionalist, to believe just is to be in a
state that plays (something like) this sort of causal role.

As the list of names of the previous paragraph suggests,
functionalism is compatible with either a representationalist approach
to belief (as in Fodor) or an interpretationist one (as in
Dennett). (The interpretationist, of course, will have to treat the
relevant functional states as posits of an interpretative theory or
scheme.) Dispositional accounts of belief, too, can be
functionalist. Indeed, dispositional accounts can be seen as a special
or limiting case of functional accounts. To see this, it's helpful to
divide the causal relations appealed to by functionalism into the
backward-looking and the
forward-looking. Backward-looking causal relations pertain to
what actually, potentially, or typically causes the state in
question; forward-looking causal relations pertain to what
effects the state in question actually, potentially, or
typically has. Thus (1) and (2) above are backward-looking causal
relations, while (3) and (4) are forward-looking. We might, then, see
the dispositionalist as a functionalist who thinks only the
forward-looking causal relations are definitive of belief: To believe
is to be in a state apt to cause such-and-such behavioral (or other)
manifestations. (This view is, of course, compatible with accepting
the existence of regularities like (1) and (2), as long as they are
not regarded as defining characteristics of belief.) Two
caveats, however, should accompany this reduction of dispositionalism
to functionalism: First, insofar as functionalism about belief
requires a causal relationship between the belief state and
its manifestations in behavior (or in other mental states), it will
exclude dispositionalists like Ryle (1949) who don't view the
disposition-manifestation relationship causally (for discussion, see
Prior 1983; Armstrong, Place, and Martin 1996; Mumford 1998). Second,
the liberal dispositionalist may wish to demur from the
functionalist's usual commitment to the reducibility of facts about
functionally-definable mental states, en masse and in
principle (allowing for the intricate network of interrelationships
among them), to facts about sensory inputs and outward behavior.

The compatibility of functionalism and representationalism is not
evident on its face, though a number of prominent contemporary
philosophers appear to embrace both positions (e.g., Fodor 1968, 1975,
1981, 1990; Armstrong 1973; Harman 1973; Lycan 1981a, 1981b; Stalnaker
1984; Lewis 1994). As Millikan (1984), Papineau (1984), and others
have suggested, it seems one thing to say that to believe is to be in
a state that fills a particular causal role, and it seems
quite another to say that beliefs are essentially states that
represent how things stand in the world. How can something
represent the world outside simply by virtue of playing a certain
causal role in a cognitive system? Suppose, for example, that a
state represents by virtue of having an indicator function of the sort
described at the end of §1.1 above. The indicator function of
an internal state or system would seem, at least sometimes and in
part, to depend constitutively on the evolutionary history of that
state or system, or its learning history, and not simply on the causal
relationships it is currently disposed to enter. Despite the
word “function” in “functionalism”, it's not clear that standard
functionalist accounts, limited as they are to appeal to a state's
actual, potential, or typical causal roles, can incorporate facts
about a system's evolutionary or learning-history: Conceivably, for
example, two states in different individuals may have exactly
analogous causal roles, yet differ in their (as Millikan says) “proper
function” because of differences in the evolutionary or learning
history of those systems.

Three escapes from this potential difficulty suggest themselves. One
is to endorse a version of “conceptual [or functional] role semantics”
according to which the representational status and content of a mental
state is reducible just to facts about what is apt to cause and to be
caused by the mental state in question—that is, to deny the
relevance of remote evolutionary or learning history to mental
representation as not part of a proper functional characterization
(e.g., Harman 1973, 1987). Another is to accept that causal role
determines the representational status of a mental state
(i.e., that it is a representation) but does not fully
specify representational content (i.e. how that
representation represents things as being); but this seems to involve
abandoning full-blown functionalism. A third is to interpret more
liberally what it is for a mental state to be “typically caused” (or
perhaps “normally caused”) by some event or state of affairs: Perhaps
it is enough that in the young organism, or its evolutionary
ancestors, mental states of that sort were caused in a particular way,
or the system was selected to be responsive to certain sorts of
environmental factors. Such claims may be more easily reconcilable
with certain canonical statements of functionalism (such as Lewis
1980) than with others (such as Putnam 1975). Although one might
suspect that most functionalist representationalists would choose the
last of these three options, the issue has not been as fully discussed
as it should be.

Some philosophers have denied the existence of beliefs
altogether. This view, generally known as eliminativism, has
been most prominently advocated by Churchland (1981) and Stich (in his
1983 book; he subsequently moderated his opinion). On this view,
people's everyday conception of the mind, their “folk psychology”, is
a theory on par with folk theories about the origin of the universe or
the nature of physical bodies. And just as our pre-scientific theories
on the latter topics were shown to be radically wrong by scientific
cosmology and physics, so also will folk psychology, which is
essentially still pre-scientific, be overthrown by scientific
psychology and neuroscience once they have advanced far enough.

According to eliminativism, once folk psychology is overthrown,
strict scientific usage will have no place for reference to most of
the entities postulated by folk psychology, such as belief. Beliefs,
then, like “celestial spheres” or “phlogiston”, will be judged not
actually to exist, but rather to be the mistaken posits of a radically
false theory. We may still find it convenient to speak of “belief” in
informal contexts, if scientific usage is cumbersome, much as we still
speak of “the sun going down”, but if the concept of belief does not
map onto the categories described by a mature scientific understanding
of the mind, then, literally speaking, no one believes anything.

Instrumentalists about belief regard belief attributions as
useful for certain purposes, but hold that there are no definite
underlying facts about what people really believe, or that beliefs are
not robustly real, or that belief attributions are never in the
strictest sense true (these are not exactly equivalent positions,
though they are closely related). One sort of
instrumentalism—what we might call hard
instrumentalism—denies that beliefs exist in any
sense. Hard instrumentalism is thus a form of eliminativism, conjoined
with the thesis that belief-talk is nonetheless instrumentally useful
(e.g., Quine 1960, p. 221 [but for a caveat see p. 262–266]). Another
type of instrumentalism, which we might call soft
instrumentalism, grants that beliefs are real, but only in a less
robust sense than is ordinarily thought. Dennett (1991) articulates a
view of this sort. Consider as an analogy: Is the equator real? Well,
not in the sense that there's a red stripe running through the Congo;
but saying that a country is on the equator says something true about
its position relative to other countries and how it travels on the
spinning Earth. Are beliefs real? Well, not perhaps in the sense of
being representations stored somewhere in the mind; but attributing a
belief to someone says something true about that person's patterns of
behavior and response. Beliefs are as real as equators, or centers of
gravity, or the average Canadian. The soft instrumentalist holds that
such things are not robustly real (if that makes
sense)—not as real as mountains or masses or individual, actual
Canadians. They are in some sense inventions that capture something
useful in the structure of more robustly real phenomena; and yet at
the same time they are not mere fictions. Soft
instrumentalism in this sense comports naturally with approaches to
belief such as dispositionalism and interpretationism, to the extent
those positions treat belief attribution simply as a convenient means
of pointing toward certain patterns in a subject's real and
hypothetical behavior.

For further discussion of eliminativism and the
considerations for and against it, see the entry on
eliminative materialism.

Philosophers often distinguish dispositional from
occurrent believing. This distinction depends on the
more general distinction between dispositions and
occurrences. Examples of dispositional statements
include:

(1a) Corina runs a six-minute mile,

(1b) Leopold is excitable,

(1c) salt dissolves in water.

These statements can all be true even if, at the time they are
uttered, Corina is asleep, Leopold is relaxed, and no salt is actually
dissolved in any water. They thus contrast with statements about
particular occurrences, such as:

(2a) Corina is running a six-minute mile,

(2b) Leopold is excited,

(2c) some salt is dissolving in water.

Although (1a-c) can be true while (2a-c) are false, (1a-c) cannot be
true unless there are conditions under which (2a-c) would be
true. We cannot say that Corina runs a six-minute mile unless
there are conditions under which she would in fact do so. A
dispositional claim is a claim, not about anything that is actually
occurring at the time, but rather that some particular thing is
prone to occur, under certain circumstances.

Suppose Harry thinks plaid ties are hideous. Only rarely does the
thought or judgment that they are hideous actually come to the
forefront of his mind. When it does, he possesses the belief
occurrently. The rest of the time, Harry possesses the belief only
dispositionally. The occurrent belief comes and goes, depending on
whether circumstances elicit it; the dispositional belief endures. The
common representationalist warehouse model of memory and belief
suggests a way of thinking about this. A subject dispositionally
believes P if a representation with the content P is
stored in her memory or “belief box” (in the central,
“explicit” case: see §2.2). When that representation
is retrieved from memory for active deployment in reasoning or
planning, the subject occurrently believes P. As soon as she
moves to the next topic, the occurrent belief ceases.

As the last paragraph suggests, one needn't adopt a dispositional
approach to belief in general to regard some beliefs as dispositional
in the sense here described. In fact, a strict dispositionalism may
entail the impossibility of occurrent belief: If to believe something
is to embody a particular dispositional structure, then a thought or
judgment might not belong to the right category of things to count as
a belief. The thought or judgment, P, may be a
manifestation of an overall dispositional structure
characteristic of the belief that P, but it itself is not
that structure.

Though the distinction between occurrent and dispositional belief is
widely employed, it is rarely treated in detail. A few important
discussions are Price (1969), Armstrong (1973), Lycan (1986), Searle
(1992), and Audi (1994). David Hume (1740) famously offers an account
of belief that treats beliefs principally as occurrences (see the
section on Causation: The Positive Phase in
Hume), in which he is partly followed by
Braithwaite (1932–1933).

It seems natural to say that you believe that the number of planets
is less than 9, and also that the number of planets is less than 10,
and also that the number of planets is less than 11, and so on, for any
number greater than 8 that one cares to name. On a
simplistic reading of the representational approach, this presents a
difficulty. If each belief is stored individually in
representational format somewhere in the mind, it would seem that we
must have a huge number of stored representations relevant to the
number of planets—more than it seems plausible or necessary to
attribute to an ordinary human being. And of course this problem
generalizes easily.

The advocate of the maps view of representational structure (see
§1.1.1, above) can, perhaps, avoid this difficulty entirely,
since it seems a map of the solar system does represent all
these facts about the number of planets within a simple, tractable
system. However, representationalists have more commonly responded to
this issue by drawing a distinction between explicit and implicit
belief. One believes Pexplicitly if a
representation with that content is actually present in the mind in
the right sort of way—for example, if a sentence with that
content is inscribed in the “belief box” (see §1.1 above). One
believes Pimplicitly (or tacitly) if one
believes P, but the mind does not possess, in a belief-like
way, a representation with that content. (Philosophers sometimes use
the term dispositional to refer to beliefs that are implicit
in the present sense—but this invites confusion with the
occurrent-dispositional distinction discussed above
(§2.1). Implicit beliefs are, perhaps, necessarily dispositional
in the sense of the previous subsection, if occurrently deploying a
belief requires explicitly tokening a representation of it; but
explicit beliefs may plausibly be dispositional or
occurrent.)

Perhaps all that's required to implicitly believe something is that
the relevant content be swiftly derivable from something one
explicitly believes (Dennett 1978, 1987). Thus, in the planets case,
we may say that you believe explicitly that the number of planets is 9
and only implicitly that the number of planets is less than 10, less
than 11, etc. Of course, if swift derivability is the criterion, then
although there may be a sharp line between explicit and implicit
beliefs (depending on whether the representation is stored or not),
there will not be a sharp line between what one believes implicitly
and what, though derivable from one's beliefs, one does not actually
believe, since swiftness is a matter of degree (see Field 1978; Lycan
1986).

The representationalist may also grant the possibility of implicit
belief, or belief without explicit representation, in cases of the
following sort (discussed in Dennett 1978; Fodor 1987). A
chess-playing computer is explicitly programmed with a large number of
specific strategies, in consequence of which it almost always ends up
trying to get its queen out early; but nowhere is there any explicitly
programmed representation with the content “get the queen out early”,
or any explicitly programmed representation from which “get the queen
out early” is swiftly derivable. The pattern emerges as a product of
various features of the hardware and software, despite its not being
explicitly encoded. While most philosophers would not want to say that
any currently existing chess-playing computer literally has the belief
that it should get its queen out early, it is clear that an analogous
possibility could arise in the human case and thus threaten
representationalism, unless representationalism makes room for a kind
of emergent, implicit belief that arises from more basic structural
facts in this way. (However, if the representationalist grants the
presence of belief whenever there is a belief-like pattern of
actual or potential behavior, regardless of underlying
representational structure, then the position risks collapsing into
dispositionalism or interpretationism.)

Empirical psychologists have drawn a contrast between implicit and
explicit memory or knowledge, but this distinction does not map neatly
onto the implicit/explicit belief distinction described in Section
2.2.1. In the psychologists' sense, explicit memory involves the
conscious recollection of previously presented information, while
implicit memory involves the facilitation of a task or a change in
performance as a result of previous exposure to information, without,
or at least not as a result of, conscious recollection (Schacter 1987;
Schacter and Tulving 1994). For example, if a subject is asked to
memorize a list of word pairs—bird/truck, stove/desk,
etc.—and is then cued with one word and asked to provide the
other, the subject's explicit memory is being tested. If the subject
is brought back two weeks later, and has no conscious recollection of
most of the word pairs on the list, then she has no explicit memory of
them. However, implicit memory of the word-pairs would be revealed if
she found it easier to learn the “forgotten” pairs a
second time. Knowledge that is “implicit” in this sense
will normally not be implicit in the sense of the previous
subsection (if it were swiftly derivable from what one explicitly
believes, presumably one could answer the test questions correctly);
it's also at least conceptually possible that some such
psychologically implicit knowledge may be stored stored
“explicitly” in the sense of the previous subsection.

A rather different empirical literature addresses the issue of
“implicit attitudes”, for example implicit racism or
sexism, which are often held to conflict with verbally or consciously
espoused attitudes. Such implicit attitudes might be revealed by
emotional reactions (e.g., more negative affect among white
participants when assigned to a co-operative task with a black person
than with a white person) or by association or priming tasks (e.g.,
faster categorization responses when white participants are asked to
pair negative words with dark-skinned faces and positive words with
light-skinned faces than vice versa). (For reviews, see Wittenbrink
and Schwarz, eds., 2007; Petty, Fazio, and Briñol, eds., 2009.)
However, it remains controversial to what extent tests of this sort
reveal subjects' (implicit) beliefs, as opposed to merely
culturally-given associations or attitudes other than full-blown
belief (Wilson, Lindsey, and Schooler 2000; Kihlstrom 2004; Lane et
al. 2007; Zimmerman 2007; Hunter 2011; Tumulty forthcoming). Gendler,
for example, suggests that we regard such implicit attitudes as
arational and automatic aliefs rather than genuine
evidence-responsive beliefs (Gendler 2008a–b; for
critique see Schwitzgebel 2010; Mandelbaum 2013).

Quine (1956) introduced contemporary philosophy of mind to the
distinction between de re and de dicto belief
attributions (as it is now generally called) by means of examples like
the following. Ralph sees a suspicious-looking man in a trenchcoat,
and concludes that that man is a spy. Unbeknownst to him, however, the
man in the trenchcoat is the newly elected mayor, Bernard J. Ortcutt,
and Ralph would sincerely deny the claim that “the mayor is a
spy”. So does Ralph believe that the mayor is a spy? There
appears to be a sense in which he does and a sense in which he does
not. Philosophers have attempted to characterize the difference
between these two senses by saying that Ralph believes de re,
of that man (the man in the trenchcoat who happens also to be the
mayor), that “he is a spy”, while he does not believe
de dicto that “the mayor a spy”.

The standard test for distinguishing de re from de
dicto attributions is referential transparency or
opacity. A sentence, or more accurately a position in a
sentence, is held to be referentially transparent if terms or phrases
in that position that refer to the same object can be freely
substituted without altering the truth of the sentence. The
(non-belief attributing) sentence “Jill kicked X”
is naturally read as referentially transparent in this sense. If
“Jill kicked the ball” is true, then so also is any
sentence in which “the ball” is replaced by a term or
phrase that refers to that same ball, e.g., “Jill kicked Davy's
favorite birthday present”, “Jill kicked the thing we
bought at Toys 'R' Us on August 26”. Sentences, or positions,
are referentially opaque just in case they are not transparent, that
is, if the substitution of co-referring terms or phrases could
potentially alter their truth value. De dicto belief
attribution is held to be referentially opaque in this sense. On the
de dicto reading of belief, “Ralph believes that the
man in the trenchcoat is a spy” may be true while “Ralph
believes that the mayor is a spy” is false. Likewise,
“Lois Lane believes that Superman is strong” may be true
while “Lois believes that Clark Kent is strong” is false,
even if Superman and Clark Kent are, unbeknownst to Lois, one and the
same person. (Regarding the Lois example, however, see §3.4, on
Frege's Puzzle, below.)

In other contexts, the liberal substitution of co-referential terms or
phrases seems permissible in ascribing belief. Shifting example,
suppose Davy is a preschooler who has just met a new teacher,
Mrs. Sanchez, who is Mexican, and he finds her too strict. Davy's
mother, in reporting this fact to his father, might say “Davy thinks
Mrs. Sanchez is too strict” or “Davy thinks the new Mexican teacher is
too strict”, even though Davy does not know the teacher's name or that
she is Mexican. Similarly, if Ralph eventually discovers that the man
in the trenchcoat was Ortcutt, he might, in recounting the incident to
his friends later, laughingly say, “For a moment, I thought the mayor
was a spy!” or “For a moment, I thought Ortcutt was a spy”. In a
de re mood, then, we can say that Davy believes, of
X, that she is too strict and Ralph believes, of Y,
that he is a spy, where X is replaced by any term or phrase
that picks out Mrs. Sanchez and Y is replaced by any term or
phrase that picks out Ortcutt—though of course, depending on the
situation, pragmatic considerations will favor the use of some terms
or phrases over others. In a strict de re sense, perhaps we
can even say that Lois believes, of Clark Kent, that he is strong
(though she would of course also simultaneously believe of him that he
is not strong).

The standard view, then, takes belief-attributing sentences to be
systematically ambiguous between a referentially opaque, de
dicto structure and a referentially transparent, de re
structure. Sometimes this view is conjoined with the view that de
re but not de dicto belief requires some kind of direct
acquaintance with the object of belief.

The majority of the literature on the de re / de
dicto distinction since at least the 1980s has challenged this
standard view in one way or another. The challenges are sufficiently
diverse that they resist brief classification, except perhaps to
remark that a number of them invoke pragmatics or conversational
context, instead of an ambiguity in the term “belief”, or in the
structure of belief ascriptions, to explain the fact that it seems in
some way appropriate and in some way inappropriate to say that Ralph
believes the mayor is a spy.

Among the more important discussions of the de re / de
dicto distinction are Quine (1956), Kaplan (1968), Burge (1977),
Lewis (1979), Stich (1983), Dennett (1987), Crimmins (1992),
Brandom (1994), Jeshion (2002), and Taylor (2002). See also
the section on the De Re/De Dicto Distinction in the entry on
propositional attitude reports.

Jessie believes that Stalin was originally a Tsarist mole among the
Bolsheviks, that her son is at school, and that she is eating a
tomato. She feels different degrees of confidence with respect to
these different propositions. The first she recognizes to be a
speculative historical conjecture; the second she takes for granted,
though she knows it could be false; the third she regards as a
near-certainty. Consequently, Jessie is more confident of the second
proposition than the first and more confident of the third than the
second. We might suppose that every subject holds each of her beliefs
with some particular degree of confidence. In general, the greater the
confidence one has in a proposition, the more willing one is to depend
on it in one's actions.

One common way of formalizing this idea is by means of a scale from 0
to 1, where 0 indicates absolute certainty in the falsity of a
proposition, 1 indicates absolute certainty in its truth, and .5
indicates that the subject regards the proposition just as likely to
be true as false. This number then indicates one's “degree of
belief”. Standard approaches equate degree of belief with the maximum
amount the subject would, or alternatively should, be willing to wager
on a bet that pays nothing if the proposition is false and 1 unit if
the proposition is true. So, for example, if the subject thinks that
the proposition “the restaurant is open” is three times more likely to
be true than false, she should be willing to pay no more than $0.75
for a wager that pays nothing if the restaurant is closed and $1 if it
is open. Consequently, the subject's degree of belief is .75, or
75%. Such a formalized approach to degree of belief has proven useful
in decision theory, game theory, and economics. Standard philosophical
treatments of this topic include Jeffrey (1983) and Skyrms (2000).

However, the phrase “degree of belief” may be misleading, because the
relationship between confidence, betting behavior, and belief is not
straightforward. The dispositionalist or interpretationist may regard
exhibitions of confidence and attitudes toward risk as only part of
the overall pattern underwriting belief ascription. Similarly,
the representationalist may hold that readiness to deploy a
representation in belief-like ways need not line up perfectly with
betting behavior. Some people also find it intuitive to say that a
rational person holding a ticket in a fair lottery may not actually
believe that she will lose, but instead regard it as an open question,
despite having a “degree of belief” of, say, .9999 that she will
lose. If this person genuinely believes some other
propositions, such as that her son is at school, with a “degree of
belief” considerably less than .9999, then it appears to follow that a rational
person may in some cases have a higher “degree of belief” in a
proposition that she does not believe than in a proposition she does
believe (see Harman 1986; Sturgeon 2008).

Philosophers have sometimes drawn a distinction between
acceptance and belief. Generally speaking,
acceptance is held to be more under the voluntary control of the
subject than belief and more directly tied to a particular practical
action in a context. For example, a scientist, faced with evidence
supporting a theory, evidence acknowledged not to be completely
decisive, may choose to accept the theory or not to accept it. If the
theory is accepted, the scientist ceases inquiring into its truth and
becomes willing to ground her own research and interpretations in that
theory; the contrary if the theory is not accepted. If one is about to
use a ladder to climb to a height, one may check the stability of the
ladder in various ways. At some point, one accepts that the ladder is
stable and climbs it. In both of these examples, acceptance
involves a decision to cease inquiry and to act as though the matter
is settled. This does not, of course, rule out the possibility of
re-opening the question if new evidence comes to light or a new set of
risks arise.

The distinction between acceptance and belief can be supported by
appeal to cases in which one accepts a proposition without believing
it and cases in which one believes a proposition without accepting
it. Van Fraassen (1980) has argued that the former attitude is common
in science: the scientist often does not think that some particular
theory on which her work depends is the literal truth, and thus does
not believe it, but she nonetheless accepts it as an adequate basis
for research. The ladder case, due to Bratman (1999), may involve
belief without acceptance: One may genuinely believe, even prior to
checking it, that the ladder is stable, but because so much depends on
it and because it is good general policy, one nonetheless does not
accept that the ladder is stable until one has checked it more
carefully.

The traditional analysis of knowledge, brought into contemporary
discussion (and famously criticized) by Gettier (1963), takes
knowledge to be a species of belief—specifically, justified true
belief. Most contemporary treatments of knowledge are modifications
or qualifications of the traditional analysis and consequently also
treat knowledge as a species of belief. (For a detailed treatment of
this topic see the entry on the
analysis of knowledge.)

There may also be types of knowledge that are not types of belief,
though they have received less attention from epistemologists.
Ryle (1949), for example, emphasizes the distinction between knowing
how to do something (e.g., ride a bicycle) and knowing
that some particular proposition is true (e.g., that Paris is
the capital of France). In contemporary psychology, a similar
distinction is sometimes drawn between procedural knowledge
and semantic, or declarative, knowledge (see Squire
1987; Schacter, Wagner, and Buckner 2000; also the entry on
memory).
Although knowledge-that or declarative knowledge may plausibly be a
kind of belief, it is not easy to see how procedural knowledge or
knowledge-how could be so, unless one holds that people have a myriad
of beliefs about minute and non-obvious procedural details. At least,
there is no readily apparent relation between knowledge-how and
“belief-how” that runs parallel to the relation epistemologists
generally accept between knowledge-that and belief-that. (For an
influential attempt to subsume knowledge-how under
knowledge-that, see Stanley and Williamson 2001; Stanley 2011.)

The standard reference text in psychiatry, the Diagnostic and
Statistical Manual of Mental Disorders (DSM-V, 2013)
characterizes delusions (e.g., persecutory delusions, delusions of
grandiosity) as beliefs. However, delusions often do not appear to
connect with behavior in the usual way. For example, a victim of
Capgras delusion—a delusion in which the subject asserts that a
family member or close friend has been replaced by an
identical-looking imposter—may continue to live with the
“imposter” and make little effort to find the supposedly
missing loved one. Some philosophers have therefore suggested that
delusions do not occupy quite the functional role characteristic of
belief and thus are not, in fact, beliefs (e.g., Currie 2000; Stephens
and Graham 2004; Gallagher 2009; Matthews 2013). Others have defended
the view that delusions are beliefs (e.g., Campbell 2001; Bayne and
Pacherie 2005; Bortolotti 2010, 2012) or in-between cases, with some
features of belief but not other features (e.g., Egan 2009; Tumulty
2011). See the entry on delusion,
especially §4.2
Are Delusions Beliefs?

The standard view that the contents of beliefs are propositions
gives rise to a debate about belief contents parallel to, and closely
related to, a debate about the metaphysics of
propositions. One standard view of propositions takes
propositions to be sets of possible worlds; another takes propositions
to have something more closely resembling a linguistic logical
structure (see
structured propositions
for a detailed exposition of this issue).

Stalnaker (1984) endorses the possible-worlds view of propositions
and imports it directly into his discussion of belief content: He
contends the content of a belief is specified by the set of
“possible worlds” at which that belief is true (see Lewis
1979 for a similar approach). The structure of belief content is thus
the structure of set theory. Among the advantages Stalnaker claims for
this view is its smooth accommodation of gradual change and of what
might, from the point of view of a discrete linguistic structure, be
seen as problematically indeterminate belief contents. Developing an
example from Dennett (1969), he describes the gradual transition from
a child's learning to say (without really understanding) that
“Daddy is a doctor” to having a full, adult appreciation
of the fact that her father is a doctor. At some point, Stalnaker
suggests, it's best to say that child “sort of” or
“half” believes the proposition in question. It's not
clear how to characterize such gradual shifts by means of a linguistic
or quasi-linguistic propositional structure (1984, p. 64–65; see
also Schwitzgebel 2001). On Stalnaker's view, the child's half-belief
is handled by attributing her the capacity to rule out some but not
all of the possibilities incompatible with Daddy's being a doctor: As
her knowledge grows, so does her sense of the excluded
possibilities.

The possible worlds approach to belief content is sometimes referred
to as a “coarse-grained” approach because it implies that any two
beliefs that would be true in exactly the same set of possible worlds
have the same content—as opposed to a “fine-grained” approach on
which beliefs that would be true at exactly the same set of possible
worlds may nonetheless differ in content. The difference between
these two approaches is brought out most starkly by considering
mathematical propositions. On standard accounts of possibility,
all mathematically true propositions are true in exactly the same set
of possible worlds—every world. It seems to follow,
on the coarse-grained view, that the belief that 1 + 1 = 2 has exactly
the same content as the belief that the cosine of 0 is 1, and thus that
anyone who believes (or fails to believe) the one accordingly believes
(or fails to believe) the other. And that seems absurd.

Stalnaker attempts to escape this difficulty by characterizing
mathematical belief as belief about sentences: The belief
that the sentence “1 + 1 = 2” expresses a truth
and the belief that the sentence “the cosine of 0 is
1” expresses a truth have different content and may differ in
truth value between possible worlds (due simply to possible variations
in the meanings of terms, if nothing else). However, it's probably
fair to say that few philosophers follow Stalnaker in this view (see
discussion in Robbins 2004; and Rayo 2013 for a recent view similar to
Stalnaker's). The apparent difficulty of sustaining such a view of
belief is often held to reflect badly on the a coarse-grained
possible-worlds view of propositions in general, since it's generally
thought that one of the principal metaphysical functions of
propositions is to serve as the contents of belief and other
“propositional attitudes” (e.g., Field 1978; Soames
1987).

Ani believes that salmon are fish; not knowing that whales are
mammals, she also believes that whales are fish. Sanjay, like Ani,
believes that salmon are fish, but he denies that whales are fish. Do
Ani and Sanjay share exactly the same belief about
salmon—namely, that they are fish—or is the content of
their belief somehow subtly different in virtue of their different
attitude toward whales? With certain caveats, the atomist
will say the former, the holist the latter. In general, the
atomist holds that the content of one's beliefs does not depend in any
general way one's related beliefs (though it may depend on the
contents of a few specially related beliefs such as definitions) and
thus, consequently, that people who sincerely and comprehendingly
accept the same sentence normally have exactly the same belief. Holism
is the contrary view that the content of every belief depends to a
large degree on a broad range of one's related beliefs, and
consequently that two people will rarely believe exactly the
same thing.

Holism may be defended by a slippery-slope argument. It seems that we
can imagine Sanjay's and Ani's beliefs about the nature of fish and
the members of the class of fish slowly diverging. At some point, it
will seem plainly correct to say that even though they may both say
“salmon are fish”, they are not expressing the same belief by that
sentence. As an extreme case, we might imagine Ani to be so benighted
as to hold that to be a “fish” is neither more nor less than to be an
Earthly animal in regular contact with Martians, and that only salmon,
whales, leopards, and banana slugs are in such contact. But if we
deny, in the extreme case, that Ani and Sanjay share the same belief,
expressed by the sentence “salmon are fish”, it seems artificial to
draw a sharp line anywhere in the progression of divergence, on one
side of which they share exactly the same belief about salmon and on
the other side of which they have divergent beliefs. One is thus led
to the conclusion that similarity in belief is a matter of degree, and
it may then be difficult to avoid accepting that even a relatively
small divergence in surrounding beliefs may be sufficient to generate
subtle differences between two beliefs expressed in the same
words. Similar slippery slope arguments can be constructed that
emphasize gradual belief change in concept acquisition (“Leibniz was a
metaphysician” agreed to before and after learning philosophy) or
gradual change in surrounding theory or in the meaning of a term
(“electrons have orbits” as uttered by Niels Bohr in 1913 and as
uttered by Richard Feynman in 1980). (This argument is similar
in some ways to Stalnaker's argument for a possible-worlds analysis of
the propositional contents of belief—see §3.1,
above—and indeed Stalnaker takes himself, there, to be committed
to holism.)

Dispositional and interpretational approaches to belief tend to be
holist. On these views, recall, to believe is to be disposed to
exhibit patterns of behavior interpretable or classifiable by means of
various belief attributions (see §1.2 and §1.3 above). It is
plausible to suppose that a subject's match to the relevant patterns
will generally be a matter of degree. There may be few actual cases in
which two subjects exactly match in their behavioral patterns
regarding P, even if it gets matters approximately right to
attribute to each of them the belief that P. Since behavioral
dispositions are interlaced in a complex way, divergence in any of a
variety of attitudes related to P may be sufficient to ensure
divergence in the patterns relevant to P itself. As Ani's
associated beliefs grow stranger, her overall behavioral pattern, or
dispositional structure, begins to look less and less like one that we
would associate with believing that salmon are fish.

It is sometimes objected to holism that, intuitively, both Shakespeare
and contemporary physicians believe that blood is red, while on the
holist view it is hard to see how their beliefs could even be similar,
given that they have so many different surrounding beliefs about both
blood and redness. Although in principle a holist could respond to
this objection by describing what sort of differences in surrounding
belief create only minor divergences and what differences create major
ones, there have been no influential attempts at such a project. It
may be possible to address the Shakespeare case by suggesting that the
content of both Shakespeare's and the contemporary physician's belief
is partly determined externalistically by the actual nature
of blood and the actual nature of redness, despite the different
conceptualizations over time (see §3.3 below). Since neither
blood nor redness have changed much since Shakespeare's day,
Shakespeare's and the contemporary physician's belief may be
similar—though, of course, if one holds them to be
exactly the same, one cannot be a holist.

Holism appears to be incompatible with a certain variety of
representationalism about belief. If beliefs, or the representations
underlying them, are stored symbols in the mind, somewhat like
sentences on a chalkboard or objects in a box (to use standard
Fodorian metaphors), then it is natural to suppose that those beliefs
can, in principle, exist independently of each other. Whether one
believes P depends on whether a representation with the
content “P” is present in the right sort of way in the mind,
which would not seem to be directly affected by whether Q or
not-Q, or R or not-R, is also
represented. If there is, in addition, an innate language of thought
of the sort advocated by Fodor and others, then the basic terms of
that language may also be exactly the same from person to person. If a
view of this sort about the mind can be sufficiently well supported,
holism would have to be rejected. Conversely, if holism is plausible,
it cuts against the more atomistic forms of representationalism.

Fodor and Lepore (1992) contains an excellent review and critique of
arguments for holism. The foremost defenders of holism are
probably Quine (1951) and Davidson (1984).

A number of philosophers have suggested that the content of one's
beliefs depends entirely on things going on inside one's head, and not
at all on the external world, except via the effects of the latter on
one's brain. Consequently, if a genius neuroscientist were to create a
molecule-for-molecule duplicate of your brain and maintain it in a
vat, stimulating it artificially so that it underwent exactly the same
sequence of electrical and chemical events as your actual brain, that
brain would have exactly the same beliefs as you. Those who accept
this position are internalists about belief content. Those
who reject it are externalists.

Several arguments against internalism have prompted considerable
debate in philosophy of mind recently. Here is a condensed
version of one argument, due to Putnam (1975; though it should be said
that Putnam's original emphasis was on linguistic meaning, not on
belief). Suppose that in 1750, in a far-off region of the
universe, there existed a planet that was physically identical to
Earth, molecule-for-molecule, in every respect but one: Where Earth had
water, composed of H2O, Twin Earth had something else
instead, “twater”, coming down as rain and filling streams, behaving
identically to water by all the chemical tests then available, but
having a different atomic formula, XYZ. Intuitively, it seems
that the inhabitants of Earth in 1750 would have beliefs about water
and no beliefs about twater, while the inhabitants of Twin Earth would
have beliefs about twater and no beliefs about water. By
hypothesis, however, each inhabitant of Earth will have a molecularly
identical counterpart on Twin Earth with exactly the same brain
structures (except, of course, that their brains will contain XYZ
instead of H2O, but reflection on analogous examples
regarding chemicals not contained in the brain suggests that this fact
is irrelevant). Consequently, the argument goes, the contents of
one's beliefs do not depend entirely on internal properties of one's
brain.

Recall that in the de dicto sense (see §2.3 above) it
seemed plausible to say that Lois Lane, who does not know that Clark
Kent is Superman, believes that Superman is strong but does not
believe that Clark Kent is strong. Despite the intuitive appeal of
this view, some widely accepted “Russellian” views in the philosophy
of language appear committed to attributing to Lois exactly the same
beliefs about Clark Kent as she has about Superman. On such views, the
semantic content of a name, or the contribution it makes to the
meaning or truth conditions of a sentence, depends only on the
individual picked out by that name. Since the names “Superman” and
“Clark Kent” pick out the same individual, it follows that the
sentence “Lois believes Superman is strong” could not have a different
meaning or truth value from the sentence “Lois believes Clark Kent is
strong”. Philosophers of language have discussed this issue, known as
“Frege's Puzzle”, extensively since the 1970s. Although the issues
here arise for all the propositional attitudes (at least), generally
the puzzle is framed and discussed in terms of belief. See the entry
on
propositional attitude reports.

A number of philosophers have argued that beings without language,
notably human infants and non-human animals, cannot have beliefs.
The most influential case for this view has been Davidson's (1982,
1984; Heil 1992). Three primary arguments in favor of the
necessity of language for belief can be extracted from Davidson.

The first starts from the observation that if we are to ascribe a
belief to a being without language—a dog, say, who is barking up
a tree into which he has just seen a squirrel run—we must
ascribe a belief with some particular content. At first blush, it
seems natural to say that, in the case described, the dog believes
that the squirrel is in the tree. However, on reflection, that
attribution may seem to be not quite right. The dog does not really
have the concept of a squirrel or a tree in the human sense. He may
not know, for instance, that trees have roots and require water to
grow. Consequently, according to Davidson, it is not really accurate
to say that he believes that the squirrel is in the
tree (at least in the de dicto sense: see §2.3
above). However, neither does the dog have any other
particular belief. Embracing holism (see §3.2 above), Davidson
asserts that to have a belief with a specific content, that belief
must be embedded in a rich network of other beliefs with specific
contents, but a dog's cognitive life is not complex enough to support
such a network. “Belief” talk thus cannot get traction (cf. Dennett
1969; Stich 1979, 1983).

Several philosophers (e.g., Routley 1981; Smith 1982; Allen 1992; Glock 2010) have
objected to this argument on the grounds that the dog's cognition
about things such as trees, while perhaps not much like ours, is
nonetheless relatively rich, involving a number of elements generally
neglected by us, such as their scent and their use in marking
territory. The dog's understanding of a tree may be at least as rich
as the human understanding of some objects about which we seem to have
beliefs. For example, it seems that a chemically untrained person may
believe that boron is a chemical element without knowing very much
about boron apart from that fact. Since we have no language for doggy
concepts, our belief ascriptions to dogs can only be
approximate—but if one accepts holism, then belief ascription to
other human beings appears to be similarly approximate.

Davidson also argues that to have a belief one must have the
concept of belief, which involves the ability to recognize
that beliefs can be false or that there is a mind-independent reality
beyond one's beliefs; and one cannot have all that without
language. However, Davidson offers little support for the claim
that belief requires the concept of belief. On the face of it, it
is not evident why this should be so, any more than having a bad temper
requires the concept of a bad temper. Furthermore, many developmental
psychologists have suggested that children do not understand the
appearance-reality distinction and do not recognize that beliefs can be
false until they are at least three years old, well after
they have begun to talk (Perner 1991; Wellman, Cross, and Watson
2001; though see Southgate, Senju, and Csibra 2007; Scott and
Baillargeon 2009). Davidson's view thus requires him either to reject
this empirical thesis or embrace the seemingly implausible view that
young three-year-olds have no beliefs (see also Andrews 2002).

The view that belief requires language is a natural consequence of the
view that belief attribution is inextricably intertwined with the
interpretation of a subject's linguistic utterances. Davidson, as
described above (§1.3), argues that the interpretation of
creature's beliefs, desires, and its language must come
together as a package. This provides a third Davidsonian reason for
rejecting belief without language (a reason that, however, remains
largely implicit in Davidson): Creatures without language are missing
part of what is essential to a behavioral pattern of the sort that can
underwrite proper belief ascription (and recall that on an
interpretational view, all there is to having a belief is having a
pattern of behavior that is interpretable in that way to an outside
observer). Any view that ties belief attribution and the subject's
language as closely together as Davidson's does—Sellars (1956,
1969), Brandom (1994), and Wettstein (2004) also offer views of this
sort—will have difficulty accommodating the possibility of
belief in creatures without language. Thus, whatever draws us to such
views will also provide reason to deny belief (or at least robust,
full-blown belief) to languageless creatures.

Positive arguments for attributing beliefs to (at least) human
infants and non-linguistic mammals have tended to focus on the general
biological and behavioral similarity between adult human beings, human
infants, and non-human mammals; the intuitive naturalness of describing
the behavior of infants and non-linguistic mammals in terms of their
beliefs and desires; and the difficulty of usefully characterizing
their mental lives without relying on the ascription of propositional
attitudes (e.g., Routley 1981; Marcus 1995; Allen and Bekoff 1997).